Ceramic arc lamp construction

ABSTRACT

An improved ceramic arc lamp construction in which the lead to the tubulation end of the lamp is a refractory metal looped member which surrounds the tubulation adjacent the end cap and is brazed thereto during assembly of the end closure components. The looped member includes a pair of leg portions which electrically connect one end of the arc tube to the arc tube mounting frame.

United States Patent [1 1 Plagge [451 Dec. 17, 1974 CERAMIC ARC LAMP CONSTRUCTION [75] Inventor: Vernon L. Plagge, East Orange, NJ.

[73] Assignee: Westinghouse Electric Corporation,

Pittsburgh, Pa.

[22] Filed: Aug. 29, 1973 21 1 Appl, No.: 392,692

[52] US. Cl 313/184, 313/217, 313/249 [51] int. Cl. H0lj l7/04 [58] Field of Search 313/25, 184, 217, 220,

[56] References Cited UNITED STATES PATENTS 3,366,828 H1968 Sygall 313/350 3,609,437 9/1971 T01 et a1. 313/220 Primary ExaminerEli Lieberman Attorney, Agent, or Firm-B. R. Studebaker [57] ABSTRACT An improved ceramic arc lamp construction in which the lead to the tubulation end of the lamp is a refractory metal looped member which surrounds the tubulation adjacent the end cap and is brazed thereto during assembly of the end closure components. The looped member includes a pair of leg portions which electrically connect one end of the arc tube to the arc tube mounting frame.

4 Claims, 4 Drawing Figures PATENTED um I 7 1974 FIG. 2.

Egg/-38 1 CERAMIC ARC LAMP CONSTRUCTION BACKGROUND OF THE INVENTION This invention relates to discharge lamps of the ceramic arc tube type and more particularly to an improved construction and method of assembly for the lower lead-in connector of such a lamp.

In a conventional ceramic discharge lamp the tubulation end of the arc tube is generally mounted toward the base of the lamp and electrical connection between the lead-in conductors and the lower electrode is generally facilitated through the tubulation. Since the round tubulation is normally tipped off after the arc tube has been exhausted and filled with the discharge sustaining filling, for example a sodium mercury amalgam, the lower lead connection has generally been made to the flattened tipped off portion of the tubulation. In this connection, a nickel strap was used to support the exhaust tube end of the arc tube and provide the electrical connection between the lead-in conductor from the stem and the lower electrode of the arc tube. The nickel strap was spot welded to the flattened section of the tantalum exhaust tubulation and was very difficult to control. In many instances, this process was believed to be the principal cause of lamp failure for the reason that during the spot welding operation the tantalum tubulation at its thinned out or flattened portion would be burnt producing either a weak spot in the thin walled, flattened, tubulation or microscopic openings both of which often result in what is known in the art as a lamp leaker. If the'welders are set to cold to avoid the burning problem equally unsatisfactory loose welds sometimes occur. An illustration of the prior art practice of spot welding the nickel support strap to the flattened pinched off portion of the exhaust and fill tubulation may be found in US. Pat. No. 3,623,134 to Werner et a1.

SUMMARY OF THE INVENTION In accordance with the present invention the above described deficiencies of the prior art structures are obviated by providing a new mounting structure and electrical connection for the tubulation end of a ceramic discharge lamp along with an improved method for assembling that end of the lamp.

The conventional arc discharge lamp of the ceramic type includes an outer bulb and a base sealed thereto with a light transmissive ceramic arc tube and an electrically conductive arc tube support structure mounted within the outer bulb and electrically connected to the lamp base. The are tube includes refractory metal end closure members with at least one of the end closure members including refractory metal exhaust and fill tubulation extending therethrough to provide access to the interior of the arc tube body during the exhaust and fill stages of the arc tube fabrication. The improvement according to this invention comprises a looped electrical lead-in conductor of refractory metal which surrounds the tubulation and is brazed thereto at its juncture with the end closure member, with the looped electrical lead-in connector including a pair of leg portions for electrically and mechanically connecting that end of the arc tube to the arc tube support structure.

The looped lead-in connector is brazed to the refractory metal tubulation during assembly of the end closure structure of the arc tube and involves inserting the refractory metal tubulation through a close fit aperture in the refractory metal end cap and, positioning a refractory metal brazing ring over the tubulation in a position contacting both the end cap and the tubulation at their juncture in the manner disclosed in US. Pat. No. 3,584,372 to D. A. Larson. To complete the assembly in accordance with this invention, the looped refractory metal support wire having mounting leg extensions is looped over the tubulation in a position contacting both the tubulation and the brazing ring adjacent the end closure member. The entire assembly is then placed in an electrically conductive holding fixture disposed in an inert atmosphere and sufficient electrical current is passed through the tubulation to cause the brazing ring to melt simultaneously sealing the end cap to the tubulation and brazing the support wire to the tubulation.

BRIEF DESCRIPTION OF THE DRAWING Many of the attendant advantages of the present invention will become more readily apparent and better understood as the following detailed description of an exemplary embodiment is considered in connection with the accompanying drawing, in which:

FIG. 1 is a side elevational view of a ceramic discharge lamp;

FIG. 2 is a side elevational view of the arc tube of a ceramic discharge lamp;

FIG. 3 is a bottom plan view of the arc tube of FIG. 2; and

FIG. 4 is one form for a fixture capable of practicing the method of this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now in detail to the drawing wherein like reference characters represent like parts throughout the several views, there is illustrated in FIG. 1 a ceramic discharge lamp constructed in accordance with the present invention. The discharge lamp generally designated 10 includes an outer envelope of glass 12 sealed to a standard mogul base 14. A pair of lead-in conductors l6 and 18 are conventionally connected to the mogul base 14 and extend through a reentrant stem press 20 at the base ofthe envelope 12 in a conventional manner. Mounted on the upper end of lead-in conductor 18 is an arc tube support frame 22 which serves to both retain and mount the arc tube within the outer envelope as well as conduct electricity to the upper electrode of the arc tube. The are tube frame 22 is supported at its upper end within the envelope 12 by a pair of resilient spring members 24 which serve to retain the frame 22 in a central location within the outer envelope 12 through resilient contact with the inner surface of the outer envelope.

The conventional ceramic arc tube 25 includes a tubular ceramic body of polycrystalline alumina 26 closed off at each end by a pair of electrode carrying end closure members or end caps 28 and 30. The end cap 28 carries on its inner side a discharge sustaining electrode 32 and on its outer side a lead-in conductor strap 34. At the other end of the ceramic body, the end cap 30 has exhaust and fill tubulation 36 extending therethrough, which exhaust and fill tubulation carries on its innermost end discharge sustaining electrode 38. The are tube 25 may be mounted to the support frame 22 at its upper end in any of several conventional manners several of which are disclosed in US. Pat. No. 3,623,134 to Leo C. Werner et al. The support frame, in addition to supporting the arc tube within the outer envelope further serves to electrically connect the discharge sustaining electrode 32 to the lead-in conductor 18. a

The improved construction of this invention relates to the mounting and electrical connection of the lower end of the arc tube to the other lead-in conductor 16. As indicated previously, in the past a lead-in connector usually in the form of a nickel strap was spot welded at one end to the flattened, sealed off portion of the tubulation and at its other end welded to the lead-in conductor 16. This was accomplished after the arc tube was completely fabricated and the exhaust, fill and tip off operations necessary to complete the arc tube were concluded. In accordance with this invention the leadin connector and support wire 40 which serves to electrically connect the lower end of the arc tube and more particularly electrode 38 to the lead-in conductor 16 is brazed to the tubulation before the tubulation is tipped off as a part of the end closure fabrication procedure. This innovation not only provides for a more secure electrical contact but in addition eliminates the spot welding step required in the fabrication of past devices.

The assembly of the bottom closure member or more particularly, the sealing of the refractory metal end cap to the refractory metal tubulation was, in the past, performed in the manner disclosed in US. Pat. No. 3,584,372 to D. A. Larson. In accordance with the present invention an additional step is added to that procedure and as illustrated in FIG. 4 the lead-in connector 40 is brazed directly to the tubulation during the end closure brazing step. In this connection, the refractory metal tubulation 36 is inserted through a close fit aperture in the refractory metal end cap 30. A refractory metal brazing ring 41, preferably titanium, is fitted over the tubulation and positioned in the contact with both the end cap and the tubulation at their juncture. A looped lead-in connector 40, best illustrated in FIG. 3, is then slipped over the tubulation and positioned in contact with both the tubulation and the brazing ring. This assemblage of parts is then placed in an electrically conductive holding fixture which is disposed in an inert atmosphere. One end of the exhaust and fill tubulation 36 is positioned on the tapered top of a locating pin 42 held in a lower clamping bar 44. The upper clamping bar 46 is then closed and secured by one of the several securing members or bolts 48 which serve to secure the clamping bars 44 and 46 in position. With the assembly in the position indicated in FIG. 4 the power supply 50 is actuated causing current to flow through the refractory metal tubulation causing the brazing ring to heat to a temperature above its melting point thereby causing it to melt and flow around the tubulation, brazing both the end cap 30 and the lead-in connector 40 to the tubulation 36.

It is common practice to employ mil wall thickness one-eighth in. OD tantalum or niobium tubing as the exhaust and fill tubulation for ceramic discharge lamps. It is also common that the end cap be constructed of niobium and the brazing ring is generally of either niobium or titanium, more often titanium. Since nickel has a melting point lower than the titanium used as the brazing material, it is necessary to substitute a more refractory metal for the lead-in connector and support wire 40. Tungsten, molybdenum, tantalum or niobium are all acceptable with niobium being preferred. The lead-in connector and support wire 40 may be fashioned from either ribbon or wire but wire is preferred and should be formed in such a way that it will contact as much of the entire outside perimeter of the tantalum tubulation as possible. In this way, the titanium brazing ring will melt and flow completely around the circumference of the exhaust tube to make a high quality braze.

As a specific example, when a niobium or titanium brazing ring, niobium end cap, tantalum tubulation and niobium lead-in connector are employed, a current of about 200 amps for several seconds provides an excellent braze between the members. The current is provided by a power supply 50 which generally includes a high current transformer and is connected to a l 10 volt power line. The 1 10 volt line is connected to an adjustable voltage source and 10:1 step down transformer which applies approximately 8 volts to the line 52 and 200 amps to the tantalum tubulation 36. The currents required are of course dependent on the size of the tantalum tube. It is preferable that the brazing take place in a vacuum or an inert atmosphere to eliminate the adverse effects of oxidation. One method which has proved successful is to accomplish the brazing in flowing commercial grade argon at about one atmosphere pressure.

After the looped lead-in connector and support wire 40 and the end cap 30 are brazed to the tantalum tubulation 36, the electrode 38 is mounted on the interior end of the tubulation. The end cap, now completely assembled is then sealed to the end of the arc tube body 26. The are tube is then exhausted and filled with a discharge sustaining filling and the outwardly projecting end of the tantalum tubulation is pinched and sealed off at 54. The upper end of the arc tube is then secured in the expansion accommodating mount and the lead-in connector 40 in a bent configuration as illustrated in FIGS. 1 and 2 is spot welded at 56 to the lead-in conductor 16. g

The improved a'rc lamp construction and method of assembly of this invention eliminates the spot welding step previously required and which is believed to be directly responsible for many lamp failures. The rigid mount improves lamp stability and is much less likely to fail mechanically from shock or vibration. Additionally, the improved connection adjacent the intersection of the end cap and the exhaust tubulation thereby imposes far less bending moment on that juncture than when the lead-in connector is spot welded near the end of the tubulation tip off.

What is claimed is:

1. An arc discharge lamp of the ceramic arc tube type comprising;

a base,

an outer envelope sealed to said base,

a pair of lead-in conductors electrically connected to said base and extending into said outer envelope,

an arc tube mounting frame mounted within said outer envelope on one of said lead-in conductors and electrically connected thereto,

a ceramic arc tube having refractory metal end closure members closing off the ends thereof and refractory metal exhaust and fill tubulation extending from at least one end closure member, said ceramic are tube supported at its upper end on said mounting frame, and

a refractory metal looped lead-in connector, said looped lead-in connector including a looped portion and a pair of leg portions, said looped portion surrounding said tubulation and brazed thereto adjacent said end closure member and said leg portions electrically connected to said other lead-in conductor.

2. An arc discharge lamp according to claim 1 wherein said looped lead-in connector is niobium.

3. In an arc discharge lamp of the ceramic type including an outer bulb and a base sealed thereto; a light transmissive ceramic arc tube and an electrically conductive arc tube support structure mounted therein and electrically connected to said base, said arc tube including refractory metal end closure members with at least one of said end closure members including refractory metal exhaust and fill tubulation extending therethrough; the improvement comprising, a looped electrical lead-in connector of refractory metal including a loop portion and a pair of leg portions, said loop portion surrounding said tubulation and brazed thereto at its juncture with said end closure member and said leg portions electrically connecting said tubulation to said support structure.

4. An arc discharge lamp according to claim 3 wherein said looped electrical lead-in connector is nio- 

1. An arc discharge lamp of the ceramic arc tube type comprising; a base, an outer envelope sealed to said base, a pair of lead-in conductors electrically connected to said base and extending into said outer envelope, an arc tube mounting frame mounted within said outer envelope on one of said lead-in conductors and electrically connected thereto, a ceramic arc tube having refractory metal end closure members closing off the ends thereof and refractory metal exhaust and fill tubulation extending from at least one end closure member, said ceramic arc tube supported at its upper end on said mounting frame, and a refractory metal looped lead-in connector, said looped lead-in connector including a looped portion and a pair of leg portions, said looped portion surrounding said tubulation and brazed thereto adjacent said end closure member and said leg portions electrically connected to said other lead-in conductor.
 2. An arc discharge lamp according to claim 1 wherein said looped lead-in connector is niobium.
 3. In an arc discharge lamp of the ceramic type including an outer bulb and a base sealed thereto; a light transmissive ceramic arc tube and an electrically conductive arc tube support structure mounted therein and electrically connected to said base, said arc tube including refractory metal end closure members with at least one of said end closure members including refractory metal exhaust and fill tubulation extending therethrough; the improvement comprising, a looped electrical lead-in connector of refractory metal including a loop portion and a pair of leg portions, said loop portion surrounding said tubulation and brazed thereto at its juncture with said end closure member and said leg portions electrically connecting said tubulation to said support structure.
 4. An arc discharge lamp according to claim 3 wherein said looped electrical lead-in connector is niobium. 